The RNA binding protein Imp is transported to axons upon developmental remodeling
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Imp is required for axonal regrowth and branching, but not for initial axonal growth
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The 3′ UTR of profilin mRNA is essential for Imp binding and axonal targeting
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imp and profilin act in the same genetic pathway to control axonal growth
Summary
Neuronal remodeling is essential for the refinement of neuronal circuits in response to developmental cues [1, 2, 3, 4]. Although this process involves pruning or retraction of axonal projections followed by axonal regrowth and branching, how these steps are controlled is poorly understood. Drosophila mushroom body (MB) γ neurons provide a paradigm for the study of neuronal remodeling, as their larval axonal branches are pruned during metamorphosis and re-extend to form adult-specific branches [5]. Here, we identify the RNA binding protein Imp as a key regulator of axonal remodeling. Imp is the sole fly member of a conserved family of proteins that bind target mRNAs to promote their subcellular targeting [6, 7, 8, 9, 10, 11, 12]. We show that whereas Imp is dispensable for the initial growth of MB γ neuron axons, it is required for the regrowth and ramification of axonal branches that have undergone pruning. Furthermore, Imp is actively transported to axons undergoing developmental remodeling. Finally, we demonstrate that profilin mRNA is a direct and functional target of Imp that localizes to axons and controls axonal regrowth. Our study reveals that mRNA localization machineries are actively recruited to axons upon remodeling and suggests a role of mRNA transport in developmentally programmed rewiring of neuronal circuits during brain maturation.
